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w i inneeGM A K IN GG w R O WIN dioxide that you add will become bound, the level of free SO2 will change by a fraction of the amount that is added. Free SO2 in wine ranges from about 35% to 75% of the total SO2 depending on the amount of compounds that are available in the wine to which the sulfite molecules can bind. To approximate what the ratio will be, use the 35% level for wines that are turbid or sweet and the 75% level for clean, dry wines. The higher the level of total SO2 in the wine, the higher the ratio will be, because there are fewer unbound compounds available for reacting with additional sulfur dioxide as it is added. Sulfur dioxide is also more affective if it is added less often and in greater quantities because it will be more of a shock to the microbes. For example, one addition of 30 ppm is more effective at killing microbes than two additions of 15 ppm spread several weeks apart. Figure V-a and V-b: At the endpoint of the Ripper titration, the indicator goes from colorless to blue. This is easy to see in white wines as demonstrated in the before, V-a (left) and after, V-b (right). Forms of sulfur dioxide to add Sulfur dioxide is available in its pure form as a compressed gas that can be made into an aqueous solution for wine additions. Most wineries use a stable, powdered form of sulfur dioxide called potassium metabisulfite. Potassium metabisulfite has the molecular formula of K2 S2 O5 and is 57.6% available SO2 by weight. Potassium metabisulfite is often abbreviated as KMB or sometimes PMBS or KMBS (K is the chemical symbol for potassium). It should be noted that KMB, PMBS and KMBS are abbreviations and not chemical formulas. The formula and calculations for determining how many grams of KMB you need to add for a given rise in ppm of SO2 is shown in Figures III and IV. For convenience, pre-weighed effervescent tablets are also available for additions to barrels. Some wineries prefer to use a premixed aqueous solution of sulfur dioxide rather than KMB. The liquid is typically 5% to 10% SO2 by weight and it can be purchased or made up at the winery by dissolving SO2 gas or KMB into distilled water. The liquid can be directly added to wine without mixing and the proper amount is measured volumetrically instead of weighed on a scale. There is an example of the calculation for a sulfur dioxide addition to wine in Figure IV. Sulfur dioxide is also available in another powdered form, sodium metabisulfite. Solutions of sodium metabisulfite in water make an excellent sanitizing agent for winemaking equipment but it should not be used for making additions to wine. Although it is not toxic, the sodium in sodium metabisulfite is not healthful and it is best left out of wine. Figure V-c and V-d: For red wines, the blue color of the endpoint is obscured by the red color of the wine and is less obvious, as shown in the before, V-c (left) and after, V-d (right). Figure V-e and V-f: In the aeration/oxidation method the sulfur dioxide is aspirated out of the wine sample before titration so the endpoint is not affected by the color of the wine. Before and after the endpoint are shown in figures V-e (left) and V-f (right). pr actica l win ery & vin eya r d JANUARY 20 14 59